The nonwoven fabric barrier layer of the present invention has many applications and, in fact, may be used wherever its unique liquid strikethrough resistance/air porosity relationships would be advantageous. For example, the barrier layer could be used in the manufacture of clothing, especially that made from nonwoven fabrics, where a barrier to liquid strikethrough is desired, e.g. laboratory coats, artists' smocks, hospital scrub clothes, rainwear, or the like. A high air porosity is desired for fabrics used for such clothing to provide greater comfort to the wearer. The advantages of the barrier layer of the present invention are best demonstrated where the barrier layer is a relatively separate layer of such clothing with minimal adhesive adherence to other fabric layers.
As used herein, the phrase "liquid strikethrough" refers to the passage of liquid from one surface of the barrier layer, through the barrier layer, to the other surface of the barrier layer.
U.S. Pat. No. 4,196,245 issued to Richard P. Kitson, Richard L. Gilbert, Jr., and Joseph Israel on Apr. 1, 1980, discloses a composite nonwoven fabric with superior liquid strikethrough resistance/air porosity relationship. It discloses a composite nonwoven fabric having an air permeability in excess of 100 mm.sup.3 /sec-mm.sup.2 at 12.7 mm H.sub.2 O differential pressure, and a liquid strikethrough resistance well in excess of 250 mm of H.sub.2 O. This liquid strikethrough resistance/air porosity relationship is achieved by having at least two adjacent hydrophobic plies of microfine fibers of a fiber diameter of about 10 microns or less incorportated in the composite nonwoven fabric having at least one other ply.
The present invention is directed to a barrier layer which provides superior liquid strikethrough resistance while maintaining high air porosity. The barrier layer is produced by the process of ring-rolling at least two adjacent hydrophobic, thermoplastic plies of microfine fibers. Ring-rolling is achieved by feeding the adjacent plies between an interdigitating set of grooved rolls.
Prior art workers have used ring-rolling to stretch materials. The stretching of thermoplastic materials by ring-rolling is generally done to achieve molecular orientation of the thermoplastic material in the direction of stretch, thus increasing the strength of the thermoplastic material in that direction. The ring-rolling of thermoplastic films is disclosed in U.S. Pat. No. 3,233,029 issued to Ole-Bendt Rasmussin on Feb. 1, 1966, and in U.S. Pat. No. 4,144,008 issued to Eckhard C. A. Schwarz on Mar. 13, 1979.
The production of microfine fiber, thermoplastic webs which may then be strengthened by stretching in one direction is disclosed in U.S. Pat. No. 4,048,364 issued to John W. Harding & James P. Keller on Sept. 13, 1977. U.S. Pat. No. 4,223,059 issued to Eckhard C. A. Schwarz on Sept. 16, 1980, discloses the ring-rolling of such microfine thermoplastic fiber webs in order to stretch and strengthen the webs. Ring-rolling of "web lamina" consisting of two microfine thermoplastic fiber webs separated by a layer of absorbent fibers to produce a high loft fabric is also disclosed by the Schwarz '059 patent.